The error 0x87D20417 is a generic error that means that the Download failed for some reason. The ruleengine.log is a good place to start, but you will get a much better reason for your failure in the PatchDownloader.log file. Look there for the real reason for your failure.
In your case Error 5 is Access Denied. The probable reason is that your SYSTEM account does not have the correct permissions to the share you are downloading to.
Here is an example of what you might see: Downloading content for ContentID = 237, FileName = windows-kb890830-x64-v4.4.exe.
Failed to create directory \\<server>\<share>\7ae115b8-160a-4324-8c47-a8ce324669f4.1\, error 5
ERROR: DownloadContentFiles() failed with hr=0x80070005
I hope this helps!
Scott